Conventionally, there is known a method to selectively provide each of a high-octane number fuel and a low-octane number fuel separated from a raw fuel to an internal combustion engine (Japanese Patent Laid-open No. 2007-278298, hereinafter referred to as Patent Document 1, and Japanese Patent Laid-open No 2009-144720, hereinafter, referred to as Patent Document 2). There is also known a method to prevent air from entering into a tank for storing the high-octane number fuel resulting from the fact that a volatility of the high-octane number fuel is lower compared to that of the raw fuel (Japanese Patent Laid-open No. 2009-203909, hereinafter referred to as Patent Document 3). Specifically, the device is configured to supply an evaporation fuel from a raw fuel tank to the high-octane number fuel tank, and further to a charcoal canister from the high-octane number fuel tank.